Physics of scuba diving

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Introduction

The effects of Pressure whilst Scuba diving

Scuba diving is a sport that many people enjoy but very few understand the physics behind. Physics is vital for divers, whether recreational or professional, as without an understanding of physical principles, diving would become unimaginably dangerous. Lots of interesting physics is involved in diving, the effects of buoyancy must be taken into account by divers to ensure that they have control of their bodies during a dive.

The phenomena of light and sound under the sea are also very different to those at the surface, Light is gradually filtered out as a diver descends, starting with red light each colour of the visible spectrum is lost, the last colour to be filtered out by the water column is blue (hence why many underwater pictures appear to be blue) until at around 70m all visible light has gone.

Sound travels much faster and further in the sea, this confuses the brain and means that sounds can appear to be all around a diver as the brain can only detect distance and direction of sounds by the time difference that they are detected in each ear, as the sounds travel much faster, the brain thinks that the sound must be all around, sounds also travel much further in water that in air, so quiet sounds are amplified and can lead to disorientation. (this is also why it is important for submarines to be quiet to avoid detection).

The major issue with gases is that they, in comparison to water have much lower densities. For all practical purposes, water does not compress under pressure,(it does, but not enough for Scuba divers to need to worry about), conversely, gases are easily compressible, and their properties change as pressure increases. As a result divers need to be aware of the basic physical formulae that relate to gas. (explained below.)

But, what is to worry about? Scuba tanks are filled with normal air aren't they?

For the most part, scuba tanks are filled with normal air. (a few special high oxygen mixtures are used by professional divers so that divers can spend many hours underwater but the principles and dangers remain the same)

The gas that we call 'air' is actually a mixture of many gases; the two main components are Oxygen (21%) and nitrogen (78%). Usually the most important gas is oxygen. Obviously humans must have a constant supply of oxygen in order to survive. Oxygen bonds easily with other elements and is thus able to aid the body in carrying nutrients around the body, thereby enabling life.

In spite of its abundance, at surface pressures, Nitrogen has almost no effects on the human body. All the nitrogen we breathe in, is exhaled without any changes to the gas, or the human body. A small amount is absorbed by the body, but at the surface it is not noticeable.

Another extension of Boyle's law, is that as a diver descends, the gas inside the body gets less dense, as a result the deeper a diver goes, the more able he is to sink. A diver needs to control their buoyancy however, so a scuba system usually incorporates a way to fill a suit with some air, to stop the rate of descent (usually in the form of an inflatable jacket called a buoyancy control device or BCD). As shown above, it is important that when ascending the diver releases this air from the BCD, as the gas inside will increase and cause rapid ascent, a slow controlled descent is required to allow nitrogen to be released from the body.

Conclusion

As I have shown, the effects of pressure that are experienced during Scuba diving are vitally important, and if not taken into account, could cause serious problems.

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